The electrode and nozzle of a plasma torch are directly exposed to a high temperature plasma arc. In order to prevent attrition of the electrode and the nozzle due to this high temperature, normally, cooling water is flowed through the interior of the electrode and around the exterior of the nozzle, so that the electrode and the nozzle are cooled (refer to Patent Document #1). Generally, this cooling water is fed under pressure to the torch by a pump from a water tank of a cooler unit which is installed exterior to the plasma cutting device. Within the torch, this cooling water first passes through the base end portion of the torch and enters into a water passage internal to the electrode and cools the electrode, and thereafter enters into a water passage which surrounds the outer surface of the nozzle and cools the nozzle. Thereafter, the cooling water passes through the base end portion of the torch and is expelled to the exterior of the torch, enters into a heat exchanger (which may be a radiator or chiller type heat exchanger) of the above mentioned cooler unit which dissipates the heat in the water, and then returns to the above described water tank for a second time. In this manner, the cooling water circulates around a single loop water cooling circuit, in which it passes in order from the cooler unit past the electrode and the nozzle within the torch, and then returns to the cooler unit.
In order to enhance the life of the electrode, it is considered to be effective to flow the water at high speed and at high volume in the neighborhood of a heat resistant insert (made from a high melting point metal such as hafnium or zirconium) in the tip end portion of the electrode, as close to this heat resistant insert as possible. Generally, a cooling water supply pipe which projects out from the torch base end portion is inserted deeply into a water passage internal to the electrode (a blind hole which extends from the base end surface of the electrode to a depth in the electrode tip end portion which is immediately behind the rear end of the heat resistant insert), so far thereinto as to reach near its bottom. By narrowing down the gap between the bottom surface of this water passage and the tip end surface of the pipe, the flow speed of the cooling water which passes over this bottom surface of the water passage is increased, so that the efficiency of cooling the heat resistant insert is further increased, and the life of the electrode is extended. In order to attain this objective, a technique is per se known for determining the relative position between the bottom surface of the water passage internal to the electrode and the tip end surface of the pipe with good accuracy (refer to Patent Document #2).
With regard to the nozzle as well, it is considered that the durability of the nozzle is also enhanced by this improvement of the cooling efficiency. In order to attain this objective, a technique is per se known for widening the water cooling area of the nozzle (refer to Patent Document #3).
Patent Document #1: Japanese Patent Publication 2,640,707.
Patent Document #2: U.S. Patent Publication 2005/92,718.
Patent Document #3: Japanese Laid-Open Patent Publication 2005-118816.